Ok, now I can search in the original branding.zip from the NVE-M300P.
I think it's in :
branding.zip\ui_alpine\common\ui\variable_def.ui
if it's in the navi.
I'll try to enter the WinCE from my IVA-W502R to check if I don't find the physical key button.

Because I'm new to this I would ask you which USB cable should I use to connect my laptop to NVE-M300P. I've got already a cable connected to navi (mini-USB) with the other end designed to plug USB stick. I tried to connect USB A-to-USB A cable via this but it didn't work. Do I need host-to-host USB cable or special crafted one to get connected?